The Old Firm rivalry opens new chapter
"It's life," a Celtic fan said to me in a Glasgow pub this week, and meant it.
Saturday's game with Rangers is the resumption of maybe the oldest, and fiercest rivalry in football.
Since Rangers' financial collapse four years ago, which meant the club had to start again from the bottom rung of the Scottish leagues, Glasgow has been deprived of one of its cultural touchstones - sometimes ugly, sometimes inspiring but always important to this city.
"See the sheriff court on Monday morning?" a Rangers man said to me, predicting possible trouble. "It will be bouncing! Four hundred bodies."
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He was wearing, rather bizarrely, a Croatian national team shirt, perhaps to allow him to pass through the streets without attracting too much attention, but his passion was bursting out.
"I'm Catholic. I've always been Rangers. Imagine that!"
In saying it, he touched on the fiery undercurrent of this rivalry. It cuts deep into the religious sectarianism that has scarred the west of Scotland for generations.
Much diminished these days - both clubs have turned the screw on people who sing the old partisan songs at matches - but it is still there.
The sound of Ibrox
It is not so long since the Rangers ground, Ibrox Stadium, rang to the deafening sound of the Orange anthem, The Sash My Father Wore, and at Celtic Park you would hear the full Irish Republican repertoire.
Their encounters sometimes seemed to be proxies for re-enactments of 17th century battles, as if the bitterness had been distilled and kept like a precious drink for special occasions.
But the story is much richer than that. This industrial city, where they used to build a quarter of the world's shipping, got much of its colour from the football field.
A smoke-shrouded, tough city, where the work was hard and life often punishing, found pageantry in the rivalry of these clubs.
Kids were reared on the magic; traditions were burnished down the years and passed on.
It often angered the other clubs in Scotland, of course. The Old Firm's dominance, and money, often seemed like a stranglehold.
Yet while Rangers were out of the Premiership, working their way back after financial disaster, everyone acknowledged that something had been lost.
You may not like them, but maybe you need them.
Jock Stein era
So, across the city they're preparing for a wild weekend. The clubs have played twice in cup competitions in recent years, but no-one took those games seriously.
Saturday's match is the resumption of the endless quest for domination, which has swung back and forth down the years.
Celtic's European Cup victory in 1967 - they were the first British club to win the competition - was their most glorious moment, at the peak of the Jock Stein era which made them untouchable for a while.
By the late 1980s and early 1990s, Rangers had resumed command and won the league title for nine years in a row.
That is the history that is the backdrop for this resumption of hostilities.
I spoke to Gordon Smith, an ex-Rangers player who became director of football at the club, who talked about life in the Old Firm.
He said - with ex-Celtic player Murdo MacLeod standing next to him - that the players generally got on well because they shared the understanding of what it's like to play for one of these clubs in Glasgow and face the fans in the street.
No-one who has not experienced it can quite understand.
'Little to match it'
For David Hay, a Celtic star from the Stein era, it will be a match of pulsating excitement that will lift Celtic Park.
Like old Rangers hands on the other side he will be in a crowd that will be gripped by the feeling that an old movie that has been on pause has started to run again, with a great climax not far away.
The Glasgow that these clubs feed on is a very different city from the one a previous generation of players knew, even, say, in the 1960s.
A modern, throbbing, young place with the smokestack industries gone and a different kind of life on the streets.
With that has gone some, though not all, of the sectarian bitterness that long disfigured the game here, but some things don't change.
Anyone wanting to understand how sporting passion can become a culture should be at Celtic Park at 1130 BST on Saturday. There is little that can match it.